A group of explorers in Russia have found around a billion roubles in old Soviet money at an abandoned mine, but it's all completely worthless.

The group from Saint Petersburg, who publish a blog on abandoned sites across Russia, came across the money after following rumours that large quantities of cash had been dumped in old missile silos near Moscow after the collapse of the Soviet Union, the Komsomolskaya Pravda news website reports. After travelling for several hours across rough terrain in Russia's Vladimir region, they found the mine overflowing with cash.

The site contains an estimated one billion roubles ($18m; £13.5m at current exchange rates, or $33.3m at the "official" Soviet rate in 1991) in Soviet Union banknotes of various denominations issued between 1961 and 1991, all no longer legal tender in the Russian Federation. The mine had been flooded in recent years, leaving what was essentially a swamp of banknotes bearing the face of Vladimir Lenin.